Ammoxidation of saturated hydrocarbons

ABSTRACT

Method for the production of acrylonitrile or methacrylonitrile from propane or isobutane employing a catalyst containing iron and bismuth.

Unlted States Patent [151 3,670,008 Taylor 1 51 June 13, 1972AMMOXIDATION OF SATURATED [56] References Cited HYDROCARBONS UNITEDSTATES PATENTS [72] Invent: Banwm' 3,118,928 1/1964 Garrison, Jr..260/465.3 [73] Assignee: Monsanto Company, St. Louis, Mo. ,6 7/ 1964nnings 6t 260/465 3 3,161,670 12/1964 Adams et a1. ..260/465 3 F11ed=21, 3,433,823 3/1969 McMahon ..260/465.3 [21] Appl 100,482 PrimaryExaminer-Joseph P. Brust Related Application Dam Attorney-Paul L.Passley, Richard W. Sternberg and Neal E.

Willis [63] Continuation-impart of Ser. No. 801,789, Feb. 24,

1969, abandoned. [57] ABSTRACT Method for the production ofacrylonitrile or 5? $5.31 "66376031135; methacrylonimle from propane orisobutane employing a 3 catalyst containing iron and bismuth 4 Claims,No Drawings AMMOXIDATION F SATURATED HYDROCARBONS This application is acontinuation-in-part of copending application Ser. No. 801,789 filedFeb. 24, 1969 now abandoned.

BACKGROUND OF THE INVENTION This invention relates to the ammoxidationof saturated hydrocarbons for form unsaturated nitriles, particularlyalpha, beta-ethylenically unsaturated mono-nitriles.

The value of alpha, beta-unsaturated nitriles is generally wellrecognized with acrylonitrile being among the most valuable monomersavailable to the polymer industry for producing useful polymericproducts. Acrylonitrile is useful in the preparation of syntheticfibers, synthetic rubbers and other useful plastic products.

Many processes, catalytic and non-catalytic, are known and practiced forthe manufactures of alpha, beta-unsaturated nitriles. A generallypracticed catalytic ammoxidation process comprises reacting an olefinwith ammonia and oxygen in the vapor phase in the presence of acatalyst. For the production of acrylonitrile, propylene is thegenerally used olefin reactam.

Propane is a source of carbon which is lower in cost than propylene orany other material useful as a starting material in the manufacture ofacrylonitrile. Therefore, it is readily recognized that a feasibleprocess for producing acrylonitrile directly from propane would behighly desirable.

Although some art has developed on the ammoxidation or propane to formacrylonitrile, a commercially feasible process has not heretofore beenreported because the ultimate yield of acrylonitrile obtained frompropane is relatively low. For example, U.S. Pat. No. 3,365,482discloses the use of molybdenum oxide or tungsten oxide as catalysts forthe conversion of propane to acrylonitrile. However, it is observed fromthis reference that the ultimate yield of acrylonitrile based on propaneconverted, is low. As discussed in this patent and clearly recognized inthe art, many catalysts are known which with comparative ease effect theammoxidation of olefins to form alpha, beta-unsaturated nitriles; butthat, unfortunately, saturated hydrocarbons do not have a reactivitycomparable to unsaturated hydrocarbons to form alpha, beta-unsaturatednitriles.

SUMMARY This invention is directed to a vapor phase process wherein atleast one saturated hydrocarbon, ammonia and oxygen are contacted in thepresence of a catalyst containing iron and bismuth under reactionconditions which produce unsaturated nitriles, particularly, at least inpart, alpha, beta-ethylenically unsaturated mononitriles. Particularly,this invention is useful in converting propane to acrylonitrile andisobutane to methacrylonitrile.

Accordingly, typical objects of this invention are to provide: l animproved vapor phase process for the production of unsaturated nitriles,(2) a vapor phase ammoxidation process for the for converting saturatedhydrocarbons directly to unsaturated nitriles (3) vapor phaseammoxidation processes for the production of acrylonitrile directly frompropane and methacrylonitrile directly from isobutane and, (4) acatalyst useful in the ammoxidation of saturated hydrocarbons.

Other objects, aspects and advantages of this invention will becomeapparent to those skilled in the art upon further study of thisdisclosure and the appended claims.

In accordance with this invention, in one aspect, unsaturated nitrilesare prepared from saturated hydrocarbons in a one step vapor phaseprocess comprising contacting at least one saturated hydrocarbon,ammonia and oxygen in the presence of a catalyst containing, as theessential catalytic ingredients, iron and bismuth under conditionssuitable for converting the selected saturated hydrocarbon to thedesired unsaturated nitrile.

Any saturated hydrocarbon capable of forming unsaturated nitriles may beused in the practice of the invention. The saturated hydrocarbons maycontain three to 12 carbon atoms per molecule and may be straightchained or branched.

Basically, the applicable saturated hydrocarbons may have up to 12carbon atoms per molecule and may be represented by the formula:

wherein R is hydrogen or a saturated monovalent organic hydrocarbonradical. Examples of useful saturated hydrocarbons are propane, butane,isobutane, pentane, isopentane, hexane, isohexane,3-methyl pentane,dimethylpentane, 2,3- dimethyl butane heptane, isohephtane, octane,isononane, dodecane, and the like.

One or more saturated hydrocarbons may be employed in the process at anyone time. The saturated hydro carbons employed should be substantiallyfree of unsaturated hydrocarbons for best conversion and optimum yieldof the desired unsaturated nitrile. The present invention is, therefor,not to be confused with the developed art directed to olefinammoxidation processes which unanimously teach that saturatedhydrocarbons in the olefin feed are inert to the reaction and apparentlyserve as a diluent.

While ammonia is most generally employed, other materials may beemployed. For example, ammonia may be generated in use from decomposableammonium compounds such as ammonium carbonate, or from various amines,such as methyl amine, ethyl amine and aniline. Any source of oxygen,pure or in admixture with inerts, may be employed in the process of thisinvention. Air is a satisfactory source of oxygen for use in thisinvention. The molar ratio of the saturated hydrocarbon: ammoniazoxygenemployed in the process of this invention, will generally be in therange of l:0.5:0.5 to 1:6:8 and preferably in the range of 1:l:l.5 to1:3:4.

The catalyst used in the process of this invention may comprise (i) amixture of the oxides of bismuth and iron and/or (ii) a compound orcomplex of oxygen, bismuth and iron.

The ironzbismuth atomic ratio of the catalyst effective in theconversion of saturated hydrocarbons to alpha, beta-unsaturated nitrilescan generally range from about 1:1 to about 1:10, although ratios ofiron and bismuth outside of this range can be used. The catalyst can beemployed with or without a support. When used with a support, preferablythe support comprises 10 to percent by weight of the catalyst. Any knownsupport materials can be used, such as, for example, silica, alumina,zirconia, Alundum silicon carbide, alumina-silica, pumice, and theinorganic phosphates, silicates, aluminates, borates and carbonates,stable under the reaction conditions encountered in the process in whichthe catalyst is used.

The iron and bismuth components can be formed separately and thenblended or formed separately or together in situ. As starting materialsfor the iron and bismuth components, for example, there can be used theoxides, such as iron oxide and bismuth oxide or metal salts, such as thenitrates or ammonium salts. The catalyst may contain small amounts ofphosphorus, such as phosphorous pentoxide, i.e., in an atomic ratio ofbismuth :phosphorus or from 1:1 to 10:3.

The activity of the catalyst system is enhanced by heating at anelevated temperature. Preferably the catalyst mixture is dried andheated at a temperature of from about 250 to about 650 C. for from 2 to4 hours and then calcined at a temperature from about 300 to about 900C. for from 2 to 8 hours. The calcination of the catalyst can be carriedout under air or an air-ammonia mixture containing about 10 to 20percent by volume of ammonia.

As previously stated, the process of this invention is carried out as avapor phase reaction. Accordingly, any apparatus of the type suitablefor carrying out oxidation reactions in the vapor phase may be employedfor the practice of the process.

The process may be operated continuously or intermittently, and mayemploy a fixed bed with a large particulate or pelleted catalyst, or aIto-called "fluidized" bed of catalyst with finely divided catalyst. Thelatter type is presently preferred for use with the process of thisinvention as it permits closer control of the temperature of thereaction.

The process of this invention is carried out at a temperature in therange of about 300 and up to about 650 C. Preferably, the reaction isconducted at a temperature in the range of about 350 to about 550 C.When ammoxidizing propane to yield acrylonitrile the preferred operatingtemperature is in the range of 450 to 600 C. and when ammoxidizingisobutane to methacrylonitrile such temperature is in the range of 350to 500 C.

Pressures other than atmospheric may be employed in the process of thisinvention, however, it will generally be preferred to conduct thereaction at or near atmospheric pressure, since the reaction proceedswell at such pressure and the use of expensive high pressure equipmentis avoided.

The contact time between the reactants and catalyst employed in theprocess of this invention may be selected from a broad operable rangewhich may vary from about 0.1 to about 50 seconds. The contact time maybe defined as the length of time in seconds which the unit volume ofreactant gases measured under reaction conditions is in contact with thevolume of catalyst employed. The optimum contact time will, of course,vary depending upon the hydrocarbon being reacted, the catalyst and thereaction temperature. In the case of converting propane toacrylonitrile, the contact time will preferably be within the range of0.5 to 15 seconds.

The reactor employed may be brought to the desired react temperaturebefore or after the introduction of the vapors to be reacted.Preferably, the process is conducted in a manner with the unreacted feedmaterials being recirculated. Also, the activity of the catalyst may beregenerated by contacting the catalyst with air at elevatedtemperatures.

The products of the reaction may be recovered from the effluent gas byany appropriate method and means known to the art and furtherelucidation here will be unnecessary duplication of the art.

DESCRIPTION OF PREFERRED EMBODIMENTS The following examples are given asillustrative of the invention, and, as such, specifics presented thereinare not intended to be unduly considered limitations upon the scope ofthis invention.

In the following examples, the reactor used is a concentric systemfabricated from 96 percent quartz tubing. The inner tube is la inch by12 inches and the outer tube is 1 inch diameter. The reactor unit issupported in a vertical 1 inch tube furnace. Heat control of the reactoris accomplished by fluidizing Fisher sea sand in the shell side of thereactor unit. The reaction temperatures given in the examples aremeasured by a thermocouple in the center of the reactor. Prior toentering the reactor, the reactant gases are mixed in standard Swagelockstainless steel T and introduced into the bottom of the reactor througha coarse quartz fritted tube. The effluent gases from the reactor arechromatographically analyzed.

EXAMPLE I This example illustrates the preparation of a catalystcomprising iron and bismuth in an atomic ratio of Fe:Bi of 1:1.

A first solution is prepared by dissolving 36.5 grams of Bi(NO 5H O in25 ml. of water and 2.5 ml. of nitric acid. A second solution isprepared by dissolving 30.5 grams of EeLNO -9H O in 50 ml. of water.These two solutions are mixed and 1.25 ml. of 85% H PO is added. Then100 grams of silica gel is added to the solution mixture. This mixtureis evaporated to near dryness and then dried in a vacuum oven at 120 C.for hours. The dried catalyst is then calcined under air at 500 C. for18 hours.

EXAMPLE I] Thiaexampleillustratestheutilityofthecatalystas prepared inthe preceding example for converting propane directly to arcylonitrile.

The feed to the reactor consists of propane, ammonia and air. The volumeratio of propanezammonia is 1:12 and propanezair is 1:12. The quantityof catalyst in the reactor is 5.9 grams. A run at 550 C. with a S-secondresidence time produces a 68.5 percent propane conversion, 6.1% singlepass acrylonitrile yield and 8.1% ultimate acrylonitrile yield. Thecatalyst is then further calcined under air admixed with 20 percentammonia at 500 C. for 2 hours. The variables of reaction temperature andcontact times are shown in the following table which also gives theresults of the reaction.

TABLE Acrylonitrile Reactor Propane 1 Single Ultimate 3 Contact timeTemp. conversion, pass 2 yield, yield, (see) 0.) percent percent percent1 Propane conversion percent=mols propane in feed, mols propane inetfluentXlOO mols propane in feed.

2 Acrylonitrile single pass yield percent=mols acrylonitrile in efliuentX mols propane in feed.

3 Acrylonitrile ultimate yield percent=acryl0nitrile single pass yieldpercentXlOO propane conversion percent.

EXAMPLE in Example II is repeated except that isobutane is used as thesaturated hydrocarbon instead of propane and temperatures of 375 C., 425C., 475 C. and 525 C. are employed. Contact times are 4,8 and *6seconds. Methacrylonitrile is obtained.

The bismuth-iron catalyst useful in this invention may be prepared byintimately mixing bismuth oxide and iron oxide or the hydrated oxidesobtained by the action of aqueous nitric acid on bismuth and iron. Thecatalyst may be prepared by hydrolyzing with water salts of the metals,such as the nitrates and recovering and heating the resultingprecipitate. A suitable bismuth-iron catalyst is described in U.S. Pat.No. 3,l35,783, which disclosure is hereby incorporated herein byreference.

It will be obvious to persons skilled in the art that variousmodifications may be made in the improved catalyst and process asdescribed in this application. Accordingly, it is intended that all suchmodifications which reasonably fall within the scope of the appendedclaims are included herein.

I claim:

1. A process for the preparation of acrylonitrile or methacrylonitn'lewhich comprises reacting in the vapor phase at a temperature of fromabout 300 to about 650 C. a hydrocarbon consisting essentially ofpropane or isobutane, ammonia and oxygen in the presence of a catalystconsisting essentially of a mixture of the oxides of bismuth and iron ora complex consisting of oxygen, bismuth and iron, the atomic ratio ofbismuthziron being from 1:1 to 10:1; the molar ratio of hydrocarbon toammonia to oxygen being from about l:0.5:0.5 to about 1:618.

2. The process of claim 1 wherein said catalyst is supported on silica.

3. The process of claim 1 wherein acrylonitrile is produced, saidhydrocarbon is propane and said temperature is from about 450 to about600 C.

4. The process of claim 1 wherein methacrylonitrile is produced, saidhydrocarbon is isobutane and said temperature is from about 350 to about500 C.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORECTION Patent No. 3,670,008 Dated June 1.3 1972 Inventor(s) KEITH M- TAYLOR It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 2, line 67, change "4" hours to "24-- hours Signed and sealedthis 27th day of February 1973.

(SEAL) Attest:

EDWARD M PLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents FORM PO-105O (10-69) USCOMM-DC 50376-1 69 U 5. GOVERNMENTPRINTING OFFICE: I969 O-365-33

2. The process of claim 1 wherein said catalyst is supported on silica.3. The process of claim 1 wherein acrylonitrile is produced, saidhydrocarbon is propane and said temperature is from about 450* to about600* C.
 4. The process of claim 1 wherein methacrylonitrile is produced,said hydrocarbon is isobutane and said temperature is from about 350* toabout 500* C.